Which of the following fuels would produce minimum environmental pollution?

Hydrogen is the answer. When it burns or reacts in a fuel cell, the only product at the point of use is water vapour. It emits no carbon dioxide, no sulphur dioxide and no particulate matter, which is why it is called a clean fuel.

• Diesel releases particulate matter, NOx and sulphur oxides, and its sulphur content is a major source of urban pollution.
• Kerosene is a petroleum fraction. Its combustion produces CO2, soot and unburnt hydrocarbons, so it is cleaner than coal but far from zero-emission.
• Coal is the dirtiest of the four, with ash, SO2, fly ash, mercury and the highest CO2 per unit of energy.

Core concept: emissions at the point of combustion, and how fuels differ by carbon and sulphur content. Mains angle: GS-III energy security and the decarbonisation of transport and industry. Grey hydrogen made from natural gas is not clean, so the production route matters. The National Green Hydrogen Mission, launched in 2023, aims at green hydrogen made through electrolysis using renewable power.

Trap: aspirants pick diesel or kerosene on the assumption that liquid fuels are cleaner, or forget that hydrogen's cleanliness depends on how it is produced.